How to bend the shape
Topology

First of all if you need to bend a mesh you will need proper quad based topology. This will allow also to add Subsurf Modifier later on if needed.

Here is an example how it can look:



You can make it as you want, just keep quads.

Bending:

In this method I'm gonna use Bezier Curve and Curve Modifier.

Add to your scene Bezier Curve and place it accordingly to your leaf mesh. For example:



After that add Curve Modifier to leaf mesh and select Bezier Curve as Object.



Now you can move leaf mesh or in Edit Mode change Bezier Curve shape as needed.

Blend file:



You can check my answer here for similar method:
 Bending a ping-pong racket